FIG. 5 is a sectional view showing a conventional loudspeaker. As shown in FIG. 5, a conventional loudspeaker has a structure in which voice coil unit 2 that is slidably disposed on magnetic circuit 1 is coupled to the inner circumferential end of diaphragm 3, the outer circumferential end of diaphragm 3 is coupled to frame 5 via first edge 4, and furthermore, the rear surface of diaphragm 3 is coupled to frame 5 via suspension holder 6 and second edge 7. In this structure, since first edge 4 and second edge 7 are symmetric to each other, harmonic distortion of a loudspeaker is reduced and power linearity is improved. Information of prior art document relating to the invention of this application is disclosed in, for example, Japanese Patent Unexamined Publication No. 2004-7335.
In such a loudspeaker, however, the outer diameter of second edge 7 contained in frame 5 is inevitably smaller than that of first edge 4 provided in an open part of frame 5. Therefore, it has been difficult to perfectly equalize the upper and lower amplitudes of diaphragm 3, thus making it difficult to completely suppress the harmonic distortion of a loudspeaker.